KR900000022B1 - Semiconductor laser - Google Patents

Abstract

The semiconductor laser for UHF oscillators has a laser structure including a laser active region (3) of multi-quantum well structure, cladding layers and a cap layer (2) formed on a substrate (1). Both end regions of the laser active region in the quantum well layer is converted into mixed crystal by impurity induced intermixing so that a multi-quantum well active region is sandwiched between mixed crystal regions (6,7). Impurity diffused regions are formed between the surface of the crystal and the mixed crystal regions, to form a current path and to inject carriers into the multi-quantum well region in a direction parallel to the laser active layer.

Description

Semiconductor laser

1 and 2 are cross-sectional views of a semiconductor laser according to an embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

DESCRIPTION OF SYMBOLS 1 Semi-insulating GaAs substrate 2: Undoped GaAlAs cladding layer

3: undoped superlattice laser active layer 4: undoped GaAlAs clad layer

5: undoped GaAs cap layer 6: n-type ion implantation area

7: p-type ion implantation region 8: n-type ion implantation region

9: p-type ion implantation region 10, 11: electrode

12, 13: ion implantation region implanted by the mask race method

15, 16: ion implantation zone

14: Re-grown cladding layer by molecular beam epitaxy

The present invention relates to a semiconductor laser capable of modulating at a high speed of 10 Hz or more.

One of the factors that determine the upper limit of the modulation frequency of a semiconductor laser is that the pn junction capacitance of the laser is large. As a countermeasure, a laser having a structure in which a portion of the laser active region necessary for laser oscillation is removed by etching and embedded in a material having a lower dielectric constant is disclosed by JEBowers (JEBowers et al., Appl. Phys. Lett. Vol 47 (1985) P. 78). However, since it is embedded in a semiconductor crystal, many defects occur, and as a result, the service life is shortened and it is not practical.

SUMMARY OF THE INVENTION An object of the present invention is to obtain a structure in which a semiconductor laser having a small capacity of an element so that ultra-fast modulation is possible in terms of lifetime.

In order to reduce the capacitance of the entire device, the capacitance and parasitic capacitance of the pn junction required for laser oscillation must be reduced. Therefore, the present invention is intended to have a structure in which the current flowing through the laser is limited and the structure for limiting the mode of light has no relation to the increase in capacitance.

In addition, the semiconductor laser of the present invention has proposed a method of making a multi-quantum well having a high quantum barrier and a large quantum size effect as a laser active layer, thereby enabling high density and high efficiency laser oscillation. In addition, this structure makes it possible to reduce the capacitance of the semiconductor laser element to an extremely small size and significantly increase the modulation frequency of the laser.

Hereinafter, embodiments of the present invention will be described.

Example 1

In FIG. 1, the undoped Ga is placed on the semi-insulating GaAs substrate 1_0.5-Al_0.5As cladding layer (2) (2 µm), undoped GaAs 50 mA / AlAs 50 mA superlattice active layer (3), undoped Ga_0.5Al_0.5As cladding layer 4 (2 mu m) and undoped GaAs cap layer 5 (0.2 mu m) are grown by molecular beam epitaxy method. Dose 2 × 10 Si at 2.3 MeV¹⁸Cm^-2Inject. Implant ion concentration 1 × 10¹⁸Cm^-3The area | region exceeding is shown by (6). The Al ions were then dosed at 2.3 MeV at 4 × 10.¹³Cm^-2in Inject. A region into which ions have been implanted is shown by (7). Using the same mask, Be ions are implanted with an acceleration voltage of 250 KeV. The region of high Be concentration is generally the same as in (7).

Subsequently, Si and Be are implanted into the regions 8 and 9, respectively, to form n-type and p-type electrode contact regions. At this time. By injecting a plurality of times while lowering the injection voltage, uniform n ⁺ and p ⁺ regions are obtained. After annealing at 850 DEG C for 5 hours under the As pressure, mixed crystallization is performed by mutually diffusing Group III members in the superlattices of the regions 6 and 7. The width of the ion implantation mask was selected so that the width of the superlattice active layer sandwiched between the mixed crystallized regions 6 and 7 was 0.8 to 1.5 mu m.

The p-side or n-side electrodes 10 and 11 form a stripe shape having a width of 10 µm and have a shape having a convex portion for bonding at the center portion, thereby reducing the capacity. The length of the laser resonator was 150 µm.

The capacity of the device was 1 PF or less. The threshold value of the laser oscillation was 5 mA, and the modulation characteristic at 5 mW output was 17 Hz at room temperature (3 dB reduction) and 23 Hz at 10 mW output.

The reason why such a high speed modulation characteristic is obtained is explained next. In this structure, since the carrier is not required to be perpendicular to the superlattice epitaxy layer, the barrier of the superlattice can be made sufficiently high, and the loss of carrier loss due to the overflow can be reduced. In addition, since it is not necessary to perform injection by tunnel current, the thickness of the barrier can also be sufficiently thick, and the width of the energy level of each quantum well can be prevented from being blurred by the formation of the subbands. Therefore, the change G of the gain with respect to the change of the injection carrier becomes large, and the relaxation oscillation frequency fr of the laser becomes large, so that the modulation frequency of the device can be increased.

Consider the capacitance of the device. In the pn junction, n-type and p-type ion implantation regions of several thousand microseconds face each other via a laser active layer of about 1 mu m, and are extremely small compared with a conventional laser structure. At the time of laser oscillation, the resistance between the p and n regions decreases, so that the capacitance between the injection regions 6, 8, and 7, 9 is also divided, further reducing the capacitance. All of the carrier injection is formed by ion implantation, and the entire substrate and other epitaxy layers can be undoped, thereby reducing the capacity.

For the above reason, a semiconductor laser capable of extremely high speed modulation can be obtained.

Example 2

The laser shown in FIG. On the semi-insulating GaAs substrate (1), the undoped Ga _0.5 Al _0.5 Al cladding layer (2), the undoped Ga _0.9 Al _0.1 As 60Å / AlAs 80 Å superlattice laser active layer (3), undoped Ga _0.5 AlAs clad After the layer 4 is grown, it is transferred to an ion implantation apparatus and maskless ion beam implantation is performed in the region 12 using. Next, ion implantation is performed in the region 13 using the Zn ion beam. The thickness of the layer 4 is about 500 GPa, so that Zn ions can easily reach the superlattice layer.

Again, feedback is made to the molecular beam epitaxy device to grow the undoped Ga _0.5 Al _0.5 As cladding layer 14 and the undoped GaAs layer 5. In the ion implantation apparatus, Si ions and Be ions are injected into the regions 15 and 16 and annealed at 750 ° C. to activate the ions and to perform mixed crystallization of the superlattice, and to embed the superstructure of the superlattice. Get The electrodes 10 and 11 were formed and incorporated in a high frequency mound to evaluate modulation characteristics. The modulation characteristics at 5 mW output at 150 μm length of the laser resonator were 25 dB at 20 mW 10 mW output.

Example 3

By using a molecular beam epitaxy method using a gas source, a barrier layer made of a undoped Inp having a film thickness of 2 탆 and a barrier layer made of an undoped AlInAs having a thickness of 0.5 탆 was grown on an Inp substrate which is a semi-insulator, and then the film thickness A quantum well layer made of GaInAs of 100 kW and a barrier layer made of AlInAs of 100 kW were alternately grown to form a multi-quantum well layer having a film thickness of 0.5 mu m. Again, a barrier layer made of AlInAs (film thickness of 0.5 mu m), a clad layer made of undoped Inp (film thickness of 1.5 mu m) and a cap layer made of undoped GaInAs (film thickness of 0.1 mu m) are grown.

Subsequently, the multi-quantum well was mixed and crystallized by impurity ion implantation and annealing in the same manner as in Example 1 to obtain an ultrafast modulated laser of a transverse single mode. The oscillation wavelength was 1.52 mu m and the modulation rate was 16 Hz (3 dB down).

In the usual embodiment, the film thickness of the quantum well layer was 30-200 kPa, the film thickness of the barrier layer was 20-400 kPa, and a good result was obtained. If the film thickness is thinner than this, the interaction between the wells occurs rapidly. In addition, the quantum size effect of the multi-quantum wells is drastically reduced, and the high speed and mode control are lost.

The thickness of the multi-quantum well layer is preferably 0.01 to 0.15 µm.

Claims (5)

A laser active layer 3 having a quantum well structure in which an impurity is not doped, and a semiconductor layer having a band gap larger than the energy band gap of the quantum well in the active layer 3 and which is not doped with impurities. At least two layers (2) are formed on the semi-insulating substrate (1) in a shape sandwiching the active layer (3), and by selective impurity doping, the quantum well structure of the active layer (3) The regions 6 and 7 which are part of a region other than the laser active region 3 and are in contact with the active region 3 are impurity organic mixed crystallized, and are also in the mixed crystallization regions 6 and 7 which are in contact with the active region. A semiconductor having a structure in which one of the regions orthogonal to the laser resonator direction is doped with p-type 9 and the other with n-type 8 to inject carriers into the laser active region 3. laser. A semiconductor laser according to claim 1, characterized by having means (8) (9) for supplying a current to said mixed crystallization region (6) (7). The semiconductor laser according to claim 1, wherein the substrate is Inp, and the active layer of the quantum well structure is made of GaInAs and AlInAs. The semiconductor laser according to claim 1 or 2, wherein the substrate (1) is GaAs and the active layer (3) of the quantum well structure is GaAlAs and AlAs. 3. The semiconductor laser according to claim 2, wherein said means for supplying current is processed by diffusion or implantation of impurities (8) and (9).

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